1. Technical Field
The present disclosure related to a system for controlling a speed of a railway vehicle by considering a braking characteristic, and more particularly, to a system for controlling a speed of a railway vehicle by considering a braking characteristic, which is capable of calculating a time-to-target-speed-crossing (TTTSC) in real time until when a train speed exceeds a speed of an automatic train operation (ATO) profile through a future speed estimation of the train and controlling the train speed to be interlocked with the calculated TTTSC.
2. Description of the Related Art
In case of a communication-based train control (CBTC) system that is operated by a radio communication, a protection-related control of a train is performed by an automatic train protection (ATP) device. A control related to an automatic operation such as a controlling of a train speed and the like is performed by an automatic train operation (ATO) device.
The ATP device sets an ATP speed profile, an ATP speed limit, or the like in consideration of various factors including a train speed limit at each section, a stop position according to movement authority, a safety braking model, and the like. The speed limit being set as such above is transmitted to the ATO device, and the ATO device generates an ATO speed profile in consideration of various factors such as ride comfort, a pressure-sensitive coefficient, and the like so as to prevent the train, which operates currently, from exceeding the speed limit.
An ATO speed tracking controller compares the ATO speed profile with a current speed of the train and applies a traction instruction to a traction device of the train and a braking instruction to a braking device thereof, thereby controlling the train to track the ATO speed profile.
That is, in the ATO system, in order to enable the train to operate in tracking a target speed that is the ATO speed profile being set at each operation section according to an operation strategy of the train within a range not exceeding the speed limit, the ATO speed tracking controller controls the traction device of the train and the braking device thereof.
In controlling the traction device of the train and the braking device thereof, when a current speed of the train is below a speed of a preset ATO speed profile, the ATO speed tracking controller transmits a traction instruction to the traction device to perform a control of increasing the speed of the train. On the other hand, when the current speed of the train is over a speed of the preset ATO speed profile, the ATO speed tracking controller transmits a braking instruction to the braking device of the train to perform a control of decreasing the speed of the train.
However, when the braking device of the train receives the braking instruction, a braking operation of 100% is not immediately performed due to a characteristic of the braking device and a certain time is required to obtain the braking operation of 100%. The reason for that is that a time is required for a compressed air of the braking device to flow and a mechanical gap basically exists in the braking device.
A distance in which the trains runs from receiving the braking instruction to performing the braking operation is referred to as a “free running distance,’ a running time of the train is referred to as a ‘free running time,’ and these meanings will be described in detail below.
Such a free running time is varied according to a characteristic of a braking device, the number of cars of a train, and the like. Generally, a variable voltage variable frequency (VVVF) electric rail car has a free running time of about 1.2 seconds, and a train for passengers has a free running time in the range of 5 to 9 seconds.
Typically, a braking distance of a train is a sum of an effective braking distance and a free running distance, and the free running distance refers to a distance in which a train moves for a free running time. That is, a distance, in which a train moves until an predicted braking force reaches up to 75% after a braking instruction is input to a braking device, is a free running distance, and a time required for running the free running distance is a free running time.
The effective braking distance is defined as a distance in which the train brakes and moves in a state in which a braking force is sufficiently increased over 75% of the predicted braking force.
Also, the free running distance is defined as a sum of a distance in which the train moves from a time when the braking instruction is input to the braking device to a time when no braking operates and a distance in which the train moves from a time when braking operates to a time when the braking force reaches up to 75% of the predicted braking force.
In other words, the train coasts for a certain time without an effective braking force after the braking instruction is input to the braking device of the train, and the braking force gradually increases at one point. At this point, a distance, in which the train moves until the time when the braking force being increasing reaches up to 75% of the predicted braking force, is the free running distance, and a time from when the braking instruction is input to when the braking force reaches up to 75% of the predicted braking force is the free running time.
In controlling a speed of a train, a speed control of the train is necessary in consideration of a free running time that is a characteristic of such a braking device. That is, in the ATO system, the train operates in a state in which a braking force is not substantially generated in the train even though a braking instruction is input to a braking device at a time when a current speed of the train exceeds a speed of an ATO speed profile. As a result, the train may operate in a state in which a speed of the train considerably exceeds a target speed, and, in some cases, the speed of the train may exceed an ATP speed limit to cause emergency braking.
Therefore, the present disclosure proposes a new method capable of more effectively enabling a train operation by controlling a speed of a train in consideration of a braking characteristic of the train, such as a free running time and the like in an automatic operation system of the train.